Gear hobbing machines

ABSTRACT

A gear hobbing machine comprising a rotary hob, an infeed slide carrying the hob, a hydraulic piston and cylinder assembly connected to the infeed slide and operable to advance it towards a gear blank to be hobbed, said cylinder and piston assembly discharging liquid during advance of the infeed slide through a normally open pilot operated check valve, a solenoid operated valve which normally permits of application of hydraulic pressure to the pilot of the check valve to maintain the check valve open, and a limit switch operable by the infeed slide to actuate the solenoid operated valve to cut off pressure from the pilot of the check valve and thereby to cause closure of the check valve to terminate advance of the infeed slide.

United States Patent 2 11 3,812,761 Southworth May 28, 1974 GEAR HOBBING MACHINES 2,507,725 5/1950 Lenthold 90/8 3,448,643 6/1969 Kylin 82/21 [75] lnvemorchr'stophel' Mm 3,683,558 s/1972 Oishi 51 /l65.78

Southworth, Ryton-upon-Tyne, England Primary Examiner-Andrew R. Juhasz v[73] Assignee: Machine Tool Divisional Services Assistant Examiner-Leon Gilden Limited, Coventry, England 22 Filed: May 3, 1972 [571 ABSTRACT A gear hobbing machine comprising a rotary hob, an {21] Appl' 250042 infeed slide carrying the hob, a hydraulic piston and cylinder assembly connected to the infeed slide and [30] Foreign Application Priority Data operable to advance it towards a gear blank to be May 4, 1971 Great Britain l2964/7l bobbed Said Cylinder and Piston assembly discharging liquid during advance of the infeed slide through a 52 US. Cl. 90/4, 82/21 A, 90/215 R normally p pilot operated check valve. a solenoid 51 Int. Cl B23f 5/22, B23b 21/00 operated valve which normally permits of application 58 Field of Search 90/8, 215 R; 5 l/l65.78, of hydraulic Pressure to the Pilot of the Check valve to 51 1 5 79 34 2 21 A, 4 A maintain the check valve open, and a limit switch operable by the infeed slide to actuate the solenoid oper- 5 R f r n Cited ated valve to cut off pressure from the pilot of the UNITED STATES PATENTS check valve and thereby to cause closure of the check valve to terminate advance of the infeed slide. 2,317,226 4/l943 Seyferth 5l/l65.78 2,395,544 2/1946 Galloway 51/ 165.78 2 Claims, 5 Drawing Figures PATENTEnm 28 mm 3812 761 sum 1 ur 2 119 24. Fly. 25.

1 GEAR HOBBING MACHINES It is known to arrange for arrest of the infeed motion of the slide carrying the hob of a gear hobbing machine when it has approached the gear blank sufficiently to produce a roughing cut and then to provide further infeed to enable the hob to perform a finishing cut. The position of the infeed slide during the finishing cut is critical because it determines the finished size of the work gear and this position is normally controlled by an adjustable dead stop. The radial position of the infeed slide during the roughing cut, however, is not so critical but must be readily adjustable and must be such that when the infeed slide is maintained in the roughing position there is adequate stiffness between the hob and the work gear to permit a satisfactory cutting action to be achieved.

The invention provides a gear hobbing machine comprising a rotary hob, an infeed slide carrying the hob, a hydraulic piston and cylinder assembly connected to the infeed slide and operable to advance it towards a gear blank to be hobbed, said cylinder and piston assembly discharging liquid during advance of the infeed slide through a normally open pilot operated check valve, a solenoid operated valve which normally permits of application of hydraulic pressure to the pilot of the check valve to maintain the check valve open and a limit switch operable by the infeed slide to actuate the solenoid operated valve to cut off pressure from the pilot of the check valve and thereby to cause closure of the check valve to terminate advance of the infeed slide.

One embodiment of gear hobbing machine according to the invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a side elevation of the machine,

FIGS. 2A and 2B are sectional views of a pilot operated check valve respectively showing this valve in the closed and in the open position,

FIG. 3 is a hydraulic circuit diagram and FIG. 4 is an electric circuit diagram.

The machine shown in FIG. 1 includes a casing containing an electric motor (not shown) for imparting rotation in conventional fashion to a hob 11 and to a gear blank 12 to be hobbed. The hob 11 is rotatably mounted in an infeed slide 13 which can be advanced towards the gear blank 12 and retracted from it by a pair of hydraulic piston and cylinder assemblies 14 of which, for clarity, one only is shown in FIG. 3. The gear blank 12 is carried by a slide 15 to which vertical movement can be imparted through gearing from the motor driving the hob, in conventional fashion to traverse the rotating gear blank past the rotating hob.

To advance the slide 13, liquid under pressure is applied to the left-hand end of the cylinder 16 of the assembly from a pressure inlet 17 through a solenoid operated valve 18. As the piston 19 of the assembly 14 advances, liquid is expelled from the right-hand end of the cylinder to tank through a pilot operated check valve 20 held open by a solenoid operated valve 21, and a flow control valve 23.

The flow control valve 23 ensures a steady rateof advance of the infeed slide 13. It is placed downstream of the check valve 20 and the piston 19 is provided with leakproof seals (not shown) to ensure that the infeed slide 13 will remain stationary when arrested in the roughing position as described below.

As shown in FIGS. 2A and 2B the pilot operated check valve 20 has an inlet 22 connected to the cylinder 16, an outlet 24 connected to tank through the flow control valve 23 and a pilot inlet 25 connected to the valve 21, and it contains a plunger 26 urged by a spring 27 to the position shown in FIG. 2A in which it blocks the flow of liquid from the inlet 22 to the outlet 24. When, however, pilot pressure is applied to the inlet 25 a piston 27 is advanced to the position shown in FIG. 2B in which it lifts the plunger 26 off a seat 28 to open the valve 20.

The infeed slide 13 carries actuators 29, 30 (FIG. 3) which cooperate respectively with limit switches LS1 and LS2, LS3. At the start of the machine cycle the limit switch LS1 is closed by the actuator 29. Upon momentary depression of a button PB a circuit is completed between lines L1, L2 to energize a relay R1, which closes a contact CR1 to establish a holding circuit for itself. Energization of the relay R1 moves the valve 18 to the position shown in FIG. 3 to supply liquid under pressure to the left hand end of the cylinder 16 and advance the slide 13. Closure of the contact CR1 also energizes a relay R2, through a normally closed contact LS2A of the limit switch LS2, to cause the valve2l to shift to the position shown in FIG. 3 in which it applies pilot pressure to the check valve 20 to open the valve 20.

When the slide 13 has advanced to the position appropriate for a roughing cut by the hob 11, the actuator 30 contacts the limit switch LS2 to open the contact LS2A, deenergize the relay R2 and cause the valve 21 to assume its other position in which it removes pilot pressure from the check valve 20 and causes the valve 20 to close to arrest the advance of the slide 13. At the same time a normally open contact LS2B of the limit switch LS2 is closed to energize a relay R3 to start rotation of the hob l1 and gear bank 12 and to impart vertical movement to the slide 15 to traverse the gear bank past the hob. When the slide 15 reaches the limit of its vertical travel a limit switch (not shown) is closed to energize a relay thereby causing a switch 31 (FIG. 4) to close to bypass the contact LS2A and reversing the position of the solenoid valve 18 (FIG. 3). Accordingly liquid under pressure is admitted to the port 24 of the check valve 20 to lift the plunger 26 and cause the piston 19 to move to the left to retract the slide 13. Operation of the relay also causes return of the slide 15 to its original position. This causes energization of the relay R1 to advance the slide 13 to take a finishing cut. As the limit switch LS2 is rendered ineffective by closure of the switch 31, the slide 13 advances until arrested by a dead stop 33. At the same time the limit switch LS3 is made to energize the relay R3 to cause rotation of the hob and work gear and vertical movement of the slide 15.

Thus at the end of the roughing cut, i.e., at the point when the limit switch is operated by the slide 15, the slide 13 retracts to the position where the limit switch LS1 is made, the slide 15 traverses vertically (either upwards or downwards) to its start of cut position and then the slide 13 advances, with the check valve 20 open, untilit reaches the deadstop 33 for the finishing cut.

As an alternative, at the end of the roughing cut the check valve 20 may be opened, and the slide 13 allowed to advance to its deadstop 33, when a vertical feed motion of the slide is commenced, in the direction opposite to that on the roughing cut. The machine may then be arranged to perform a climb out at a first cut and a conventional cut at a second cut.

What I claim as my invention and desire to secure by Letters Patent is:

l. A gear hobbing machine comprising a hob, an infeed slide carrying the hob and movable from an initial position to advance the slide and the hob toward a gear blank to positions appropriate for performance by the hob of roughing and finishing cuts, a piston and cylinder assembly connected to the slide to effect advance and retraction thereof, connections between opposite ends of the cylinder of said assembly to pressure and tank, a control valve controlling said connections, a pilot operated check valve interposed in one of said connections, a solenoid operated valve which normally applies pilot pressure to said check valve to maintain the check valve open, means operable at the start of a machine cycle to operate said control valve to admit liquid under pressure to said cylinder in the direction to cause said assembly to advance said slide and discharge liquid through said check valve, a limit switch positioned to be actuated by said slide when it reaches the position corresponding to the roughing cut, means responsive to actuation of said limit switch for causing said solenoid operated valve to remove pilot pressure from said check valve, thereby causing said check valve to close to prevent further advance of said slide by said assembly while liquid under pressure remains admitted to said assembly, means operative after performance of a roughing cut to reopen said check valve to permit further advance of said slide by said assembly and a stop for arresting advance of said slide when it has reached the position corresponding to the finishing cut.

2. A machine as claimed in claim 1, which includes a flow control valve positioned downstream of said check valve in the connection containing said check valve. 

1. A gear hobbing machine comprising a hob, an infeed slide carrying the hob and movable from an initial position to advance the slide and the hob toward a gear blank to positions appropriate for performance by the hob of roughing and finishing cuts, a piston and cylinder assembly connected to the slide to effect advance and retraction thereof, connections between opposite ends of the cylinder of said assembly to pressure and tank, a control valve controlling said connections, a pilot operated check valve interposed in one of said connections, a solenoid operated valve which normally applies pilot pressure to said check valve to maintain the check valve open, means operable at the start of a machine cycle to operate said control valve to admit liquid under pressure to said cylinder in the direction to cause said assembly to advance said slide and discharge liquid through said check valve, a limit switch positioned to be actuated by said slide when it reaches the position corresponding to the roughing cut, means responsive to actuation of said limit switch for causing said solenoid operated valve to remove pilot pressure from said check valve, thereby causing said check valve to close to prevent further advance of said slide by said assembly while liquid under pressure remains admitted to said assembly, means operative after performance of a roughing cut to reopen said check valve to permit further advance of said slide by said assembly and a stop for arresting advance of said slide when it has reached the position corresponding to the finishing cut.
 2. A machine as claimed in claim 1, which includes a flow control valve positioned downstream of said check valve in the connection containing said check valve. 